Field of the Invention
The present invention relates to a pod or an airtight container called FOUP (Front-Opening Unified Pod) in which wafers are housed, which is used in what is called an FIMS (Front-Opening Interface Mechanical Standard) system for transfer between semiconductor processing apparatuses. The present invention also relates to an FIMS system that also functions as a purge system that performs purging operation for cleaning the interior of the pod.
Description of the Related Art
The pod to which the present invention is directed includes a body part in which wafers are to be housed and a lid that closes the opening of the body part. The operations of opening and closing the lid of the pod and the transfer of wafers into/out of the pod are performed through a mini-environment in which a transfer robot with which a semiconductor processing apparatus is equipped is provided. A load port apparatus has a wall partly defining the mini-environment and having an opening portion leading to the mini-environment, a pod table on which a pod is placed with its opening directly facing the opening portion of the wall, and a door part that closes and opens the opening portion of the wall.
Typically, the interior of the pod loaded with wafers or the like is filled with dry nitrogen or the like gas that is controlled to be highly clean to prevent the entry of contaminants and oxidative gases etc. into the pod. However, while wafers in the pod are transferred to one of various kinds of processing apparatuses to undergo certain processing, the interior of the pod and the interior of the processing apparatus are kept in communication with each other. Consequently, the gas in the processing apparatus and the mini-environment enter the interior of the pod, and there is a possibility that oxygen and/or moisture in the gas may adhere to the surface of the wafers.
Oxidative gases such as oxygen form an ultrathin oxide film on the surface of the wafers or on the various kinds of layers formed on the wafers. There is a possibility that the presence of such an oxide film may prevent micro devices from having desired characteristics. A possible countermeasure to this is to introduce a gas with a controlled partial pressure of oxidative gas such as oxygen into the pod to prevent an increase in the oxygen partial pressure. A specific method is disclosed in Japanese Patent Application Laid-Open No. 11-307623. In the apparatus disclosed in this patent literature, a pod is provided with a tower-shaped gas supply nozzle projecting into the interior of the pod, and gas is supplied into the pod through a porous sintered material to fill the pod with inert gas.
In the apparatus disclosed in Japanese Patent Application Laid-Open No. 11-307623, the increase in the partial pressure of the oxidative gases is reduced by the supply of inert gas through the tower-shaped nozzle. It is generally the case that when wafers in the pod are to be actually subject to various processing, the lid is kept open until processing on all the wafers in the pod is completed. In this case, since down flow having high flow rate is created in the mini-environment in communication with the pod, in order to satisfactorily prevent diffusion of oxidative gases from the mini-environment into the pod, it is necessary to supply a large quantity of inert gas.
In conventional semiconductor devices, even if the flow rate of the supplied inert gas is so low as to lead to an increase in the partial pressure of oxidative gases such as oxygen, the degree of oxidation of wiring has been below a level to be addressed as a problem. However, with slimming of wiring in semiconductor devices in recent years, a further reduction in the oxygen partial pressure is required in order to prevent oxidation of thin wiring, even when the lid is kept open during consecutive wafer processing, during which no serious problem occurs with previous semiconductor devices. In view of the apparatus disclosed in Japanese Patent Application Laid-Open No. 11-307623, in order to ensure a flow rate in inert gas supply high enough to reduce the increase in the oxygen partial pressure, it is preferred that the use of a porous sintered material having a high conductance be eliminated. Supplied inert gas is introduced only one-dimensionally and only by diffusion, and therefore there may arise problems of uneven distribution of gas in purging and limited replacement efficiency.